The present invention relates to dampers for controlling the flow of fluid and more particularly to dampers of this type which employ a sliding blade member to substantially prevent the flow of fluid through a duct.
Dampers having sliding blade members have long been used to control the flow of fluids such as flue gases. For example, U.S. Pat. No. 3,728,389 (Lowe, et al,) discloses a damper having a movable curtain provided with spring seals for sealing the curtain against a frame when the curtain is drawn to extend across the frame.
Several dampers of the prior art have employed movable gates which can be positioned across a conduit to obstruct it. U.S. Pat. No. 3,069,129 (Grove), U.S. Pat. No. 3,206,162 (Bogot), U.S. Pat. No. 3,460,457 (Lowe, et al.), and U.S. Pat. No. 3,596,874 (DiSanto) provide examples of these sliding gate dampers. In each case the gate travels in guides which are open to the fluid flowing through the conduit when the damper is open. In some, such as Lowe and DiSanto, sealing is provided by resilient seals between the gate and the damper.
A third approach to the sliding blade damper is disclosed in U.S. Pat. No. 3,575,377 (Carlton) which shows a sliding blade member having an aperture defining open section and an imperforate closed section. The damper is opened or closed by appropriate positioning of the blade in the damper.
These and other sliding blade dampers of the prior art exhibit certain disadvantages which can be especially significant in applications which require substantially zero leakage in the presence of fly ash or other particulate matter. Such requirements are becoming increasingly widespread, especially in conjunction with flue gas dampers. Pollution control equipment is increasingly being used to process flue gas before it is released to the atmosphere. This equipment of course requires servicing, and it is often desirable to provide a damper capable of preventing substantially all flue gas from reaching the equipment while it is being serviced. In some cases, federal government regulations may require such dampers in order to protect personnel working in the duct. It is important that such dampers function reliably without leakage, binding, or jamming in an environment that includes large quantities of fly ash and other particulate matter.
Fly ash can build up as a cement-like mass on spring seals, thereby preventing complete sealing. Furthermore, when guides are exposed to fly ash for extended periods, as in the gate dampers described above, the build-up of fly ash can cause binding and incomplete closing of the gate in the damper. Seals, such as those used by Carlton, which are made of materials which can be damaged by high temperatures are unsuitable for many high temperature applications.